The subject invention is generally directed to swath type printers, and more particularly to apparatus and techniques for vertical and horizontal alignment of the printheads of a multiple printhead swath type printer.
A swath printer is a raster or matrix type printer that is capable of printing a plurality of rows of dots in a single scan of a movable print carriage across the print media. The print carriage of a swath printer typically includes a plurality of printing elements (e.g., ink jet nozzles) displaced relative to each other in the media motion direction which allows printing of a plurality of rows of dots. Depending upon application, the separation between the printing elements in the media scan direction can correspond to the dot pitch for the desired resolution (e.g., {fraction (1/300)}th of an inch for 300 dot per inch (dpi) resolution). After one swath or carriage scan, the media can be advanced by number of rows that the printer is capable of printing in one carriage scan or swath (i.e., the swath height or swath distance). Printing can be unidirectional or bidirectional.
The printing elements of a swath printer are commonly implemented in a printhead that includes an array of printing elements such as ink jet nozzles. Depending upon implementation, the printhead comprises a removable printhead cartridge such as those commonly utilized in ink jet printers. Throughput of a swath type ink jet printer can be increased by utilizing multiple ink jet printhead cartridges to increase the height of a swath by the additional printhead cartridges. A consideration with multiple printhead cartridge swath printers is print quality degradation as a result of printhead mechanical tolerances (e.g., the uncertainty of printhead cartridge to printhead cartridge positioning, and uncertainty of variations due to cartridge insertions), and drop velocity differences between printhead cartridges, where such degradation can occur in both bidirectional and unidirectional printing. Mechanical tolerances of the printhead to print media spacing also causes print quality degradation in bidirectional printing, with one or a plurality of printhead cartridges.
Factory compensation for each printer manufactured and/or tight manufacturing tolerance control would address some of the factors contributing to print quality degradation, but would be extremely difficult and expensive. Moreover, manufacturing tolerance control might not be able to address the effects on the printer of aging and temperature, particularly as to electronic components of the printer.
It would therefore be an advantage to provide methods and apparatus for detecting and compensating misalignments that affect print quality in a multiple printhead cartridge swath printer.
Another advantage would be to provide methods for automatically detecting and compensating misalignments that affect print quality in a multiple printhead cartridge swath printer.
In accordance with the invention, an optical sensor including a quad photodiode detector is utilized to determine the horizontal positions of printed vertical test lines which are imaged on the detector in conjunction with horizontal alignment correction, as well as the vertical positions of printed horizontal lines which are imaged on the detector in conjunction with vertical alignment correction.